(a) Field of the Invention
The present invention relates to novel thermosetting resin compositions which are excellent in impact strength and flexibility. More particularly, it relates to thermosetting resin compositions and their prepolymers having aromatic bismaleimide derivatives and diamine derivatives as structural units.
(b) Description of the Prior Art
Conventional thermosetting resins having imide structure have been widely used in industry due to their excellent properties such as electrical insulation, high-temperature stability and dimensional stability of molded articles.
The thermosetting resins, however, obtained by using aromatic bismaleimides as polymerization ingredients are insoluble and infusible, and have exhibited drawbacks of poor impact strength and flexibility, though these materials are excellent in the high-temperature stability. Therefore, as a method for improving the impact strength and flexibility of the aromatic bismaleimide resins, aromatic bismaleimides were tried to use in combination with aromatic diamines. For example, polyamino-bismaleimide resin which is composed of N,N'-(4,4'-methylenediphenylene)bismaleimide and 4,4'-diamino-diphenylmethane (trade mark KERIMID, a product from Rhone-Pulenc Ind.) has superior impact strength and flexibility to the homopolymers of aromatic bismaleimide. Therefore the resin is used for impregnation varnish, laminated boards, molded articles, etc.
The above thermosetting resins, however, have been still unsatisfactory in the impact strength and flexibility view point.